The present invention is directed to a magnetic tape cassette comprised of upper and lower cassette halves and, in particular, to an improved structure of a projection formed internally of and integrally with the lower cassette half and disposed between two reels.
Conventional magnetic tape cassettes, as used in audio equipment, video equipment and the like, include a magnetic tape wound around two reels rotatably supported within the cassette case to achieve recording and reproduction.
In such conventional cassettes, the reels or tape winding members are rotatably supported between upper and lower cassette halves, each of the cassette halves being formed from a synthetic resin such as ABS or the like.
There has been an increasing demand for reductions in the weight of the magnetic tape cassette to improve the handling of the cassette and in manufacturing costs. Since the cassettes are mass produced, even a small reduction in weight would prove advantageous.
In order to reduce the weight of a magnetic tape cassette, it is necessary to employ various thicker portions and thinner portions within the cassette. However, since the fluidity of the fused resin is limited when injected, it is difficult to transmit an injection pressure to create these portions. Thus, with respect to a projection (which will be described in detail later) formed within the cassette, a sink or deformation may result due to increased shrinkage of the resin. Since it is difficult to correct the shrinkage, as compared to remaining portions of the cassette, the deformation or sink will remain, forming a significant defect.
FIG. 4 shows a perspective view of one type of conventional lower cassette half 1 for use in a VHS system, and FIG. 5 shows a perspective view of an internal surface of the same lower cassette half 1. The lower cassette half 1 includes right and left drive shaft insertion openings 7, a sensor insertion hole 10 for insertion of a light source which, when inserted, extends along center line C of the cassette so as to emit light in the right and left directions to detect the end of the magnetic tape, a threaded boss hole 11 for accepting a screw to fasten the upper and lower cassette halves together, and a guide groove 9 for guiding the alignment of the upper and lower half cassettes so that they can easily be connected together.
A tongue-shaped projection 32 is provided on the back side of the guide groove 9, that is, on the inner surface of the lower cassette half 1 in the vicinity of a partition wall 5 disposed in the front portion of the cassette, as shown in FIGS. 2 and 3. The projection 32 extends rearwardly from a boss 31 in which the above-mentioned boss hole 11 is formed. As is clearly illustrated in FIG. 3, which is an enlarged perspective view showing the projection 32 from inside the cassette, the projection 32 functions as a support material for forming the guide groove 9. Structures such as the projection 32 and the boss 31, which can increase the thickness of the case, are localized at a certain position within the cassette so that differences in thickness and mass distribution at the localized areas, as compared to the remaining portions, are increased.
Since it is desirable to reduce the thickness of the portions surrounding the shaft insertion openings 7, in order to reduce the weight of the cassette case, the differences in thickness between the projection 32 and its neighboring portions may be even further exaggerated.
As noted above, a deformation or sink mark may be formed in the vicinity of the projection 32 as a consequence of the reduction in thickness of portions of the cassette. The sink mark impairs the appearance of the surface of the finished product as well as its commercial value. Also, it is difficult to obtain an even mechanical strength in these portions. Further, since such deformations are usually located at or near a portion which forms the guide groove 9, as described above, even a slight deformation can make it difficult to insert the cassette into a bucket of the VCR or other recording/playback device.